Terry,
I will respond to you comments as best I can.
Terry Harris wrote:
> On Fri, 27 Apr 2001 20:07:30 -0700, Jim McGrath wrote:
>
> >> I hope it isn't that simple - testers, particularly roving probe testers
> >> only test continuity from each end of a 'net' + any stubs. For testing
> >> non-continuity (shorts) they don't bother looking for shorts between nets
> >> which don't get close to each other. You need more than a netlist and pad
> >> locations to figure out net ends, stubs, and net proximity
> >
> >This is confusing me. If they dont get close to each other how is it a short?
>
> Sorry, do we talk about testers testing to make sure you have what you
> want or to make sure you don't have what you don't want?
I believe what we want. The database and all its rules should prove what we don't
want. Ie spacingViolations track to track for matched pairs etc. We need to have
that all in place, and the test at fab is only a continuity check.
> >> Much needed?
> >
> >Yes it is Much needed.
> >>
> >> While Gerber is not an ideal format for generation of connectivity
> >> information at least it is a standard and one that PCB houses are going to
> >> get from all customers.
>
> >That is a MAJOR problem. This File Needs to come fron the database
> >so it verifys the gerbers. I have been almost bitten and the D-356 saved me.
>
> But it doesn't verify the gerbers until the PCB is made and on the tester -
> too late. Also you are responsible for making sure the Gerbers and D-356
> files are correct (apart from screw ups the board house makes plotting
> which are maybe their problem).
>
My experience is the better Fab houses compare the Gerbers to the IPC
Prior to fabrication. I have that as a requirement in the fab notes.
> Why should it be easier to make a correct bug free D-356 generator than a
> correct bug-free Gerber generator?
As I indicated in my original post there are times I must manipulate the gerbers.
The IPC File verifys I did it correctly.
>
>
> >> If you choose to supply the board house with additional information then it
> >> is your problem if it is wrong - and you are going to be less familiar than
> >> the board house is with the conversion tool and less able to 'tune' it to
> >> suit their tester
> >
> >Not if it is pulled directly from the database. The Gerbers can be wrong for
> >many reasons.
>
> And why can't D-356 files be wrong? Gerbers come from the database too.
Yes Im sure that could be true, but my track record indicates the contrary. Also see
above.
>
>
> >> I think it would be more useful to be able to check a conectivity netlist
> >> against a Protel design, the PCB house gives you the netlist generated from
> >> Gerbers the way they think they plotted them. That would check the
> >> connectivity netlist and Gerbers and check them before they have made a
> >> batch of possibly bad PCBs.
>
> >Yes this would work but... I have TOO much work as it is and I'm not getting
> >paid to verify the Board houses work. I can Prove the IPC file does this and puts
> >the responsiblity in the board houses hands where it belongs.
>
> Are getting paid to produce D-356 files for the board house doing their
> work for them?
I paid for the 3rd party software and charge a fee for the netlist generation.So, Yes
I am.
>
>
> You can't *prove* anything. If the boards fail on test it could be the
> D-356 file - your fault, or the gerbers which could be your or their fault,
> or manufacturing problems which are likely their fault. Or the Gerbers and
> D-356 could be similarly wrong which wont fail test at all and be your fault.
I don't believe this to be true. If you get the match of the IPC to gerbers then its
in fab houses hands.
I also feel I am missing something about the testing you are doing. I am talking
about bare board test only. Not assembled test. Am I missing the point?
>
> A netlist from a third party tool analysing a gerber (particularly if it is
> part of the CAM package the board house is using to plot) is a better cross
> check. A netlist compare (fed back to the CAD package or external from an
> additional netlist from the CAD package) will show problems before you make
> and waste boards.
That IS the purpose of the IPC File but in the reverse of you example you state.
Again back in the fab houses hands.
>
> That is why I suggest the board house ought to be doing the work from
> Gerbers with a tool they understand and matches their plotting and testers.
> If you want to feed a netlist in what ever format to or from the board
> house for cross checking before PCBs are manufactured that is cool.
I am verifying the gerbers with the IPC file. I have YEARS of use of this process
and feel it is stable and will become even more important in the future.
> I would go along with a D-356 export or DRC check for Protel but only for
> use as a cross check not for actual board testing (well not till P2002SE
> +SP? anyway).
Me Too.
>
>
> Cheers, Terry.
>
Hope this clears up any confusion about my earlier post.
Regards,
Jim.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To join or leave this list visit:
* http://www.techservinc.com/protelusers/subscrib.html
* - or email -
* mailto:[EMAIL PROTECTED]?body=leave%20proteledaforum
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
